The present invention relates to a personnel monitoring system, and more particularly to an Electronic House Arrest Monitoring (EHAM) system that monitors individuals wearing a special electronic tag for compliance with a court order (or other mandate) to remain at a specified location, even when conventional telephone service is not available at the specified location. Further, the invention relates to a unique cellular interface unit that may be used to convert an EHAM system that requires a telephone line installed at the house arrest monitoring location to an EHAM system that does not require a telephone line installed at the house arrest monitoring location.
Electronic house arrest monitoring systems are known in the art. See, for example, U.S. Pat. No. 4,918,432, assigned to the same assignee as is the present application, which patent is incorporated herein by reference. The EHAM system described in the '432 patent is known as an "active" EHAM system, in that it utilizes an electronic tag, worn by the individual being monitored, which periodically, e.g., every minute, transmits a unique identification (ID) signal that identifies its wearer. The ID signal is transmitted at low power, and hence is only receivable over a relatively short range, e.g., 150 feet. A Field Monitoring Device (FMD) is placed at the location where the monitoring of the individual occurs (the "house arrest location"), usually the residence and/or work place of the person being monitored. The FMD includes a receiver circuit adapted to receive the ID signal when the tag is within range thereof, i.e., when the person being monitored is at the house arrest location. The FMD also includes memory circuits suitable for keeping track of when the ID signal is received and when it is not, and thus when the monitored person is present at or absent from the house arrest location.
The FMD is coupled, through conventional telephone lines, to a host computer at a location remote from the house arrest location. The host computer is maintained by a governmental or other agency charged with the responsibility of carrying out the monitoring function. The host computer typically monitors several FMD's at numerous house arrest locations. From the information received from the FMD's, the host computer can periodically, or on request, generate appropriate reports indicating the presence or absence of the monitored person at specified house arrest locations over a specified period of time. From such reports, the monitoring agency can readily determine if the person is in compliance with a court order or other mandate to remain, or report in, at a particular house arrest location at specified times of the day.
Advantageously, the type of EHAM described in the '432 patent also includes the ability to detect any attempt by the person being monitored to tamper with the FMD or the tag. If a tamper event is detected, then the FMD makes contact with the host computer as soon thereafter as possible and reports such detected tamper. Further, the host computer may randomly make contact with the FMD to check on its operation. If contact cannot be made, e.g., if the FMD has been disconnected, destroyed or otherwise rendered nonfunctional, or if the telephone lines have been cut, then such lack of contact is noted and reported as a possible tamper event. Any reported tamper events may thus be manually checked out by the monitoring agency as needed, e.g., by having a parole officer or other individual go to the house arrest location and verify that the person being monitored is there and that the tag and FMD are functioning properly.
Numerous variations and adaptations of the basic active EHAM system are also known in the art. See, e.g., U.S. Pat. No. 4,952,928, also assigned to the assignee of the present application, and incorporated herein by reference.
In addition to active EHAM systems, "passive" EHAM systems are also known in the art, e.g., as shown in U.S. Pat. No. 4,747,120. In a passive system, there is no ID signal that is transmitted on a regular basis. Rather, the person being monitored must perform some act, e.g., as instructed over the telephone, at the house arrest location, such as inserting a specially coded wristlet into a decoder, placing a thumb or finger into an electronic fingerprint device, speaking certain words into the telephone, etc. Such acts, if properly done by the correct individual, cause a verification signal, or equivalent, to be generated, which verification signal is received at the host computer, thereby signalling the host computer that the correct individual is at the house arrest location at the time the act was performed.
Both the passive and active EHAM systems known in the art require that the person being monitored have a telephone line installed at the house arrest location, typically their residence. Unfortunately, many individuals who could be placed under house arrest do not have a telephone line installed, or if a telephone line is installed, it is a "party line" or other joint-use line that is not suitable for use full-time with an EHAM system. Hence, there is a need in the art for an EHAM system that is able to perform the desired monitoring function without the need of an installed telephone line at the house arrest monitoring location.
Cellular telephone units are known in the art, and provide a convenient alternative to a conventional telephone line. A cellular telephone unit typically includes a handset of some sort, similar to a conventional telephone, that allows its user to both talk and listen, as well as dial a desired telephone number. Cellular units include an RF transceiver that is coupled to a cellular telephone network that "covers" (i.e., is able to receive and send cellular RF signals over) an extensive geographical area (the RF "range" of the cellular network). The cellular telephone network, in turn, is coupled to a conventional telephone network managed by one or more local telephone companies. Hence, a person with a cellular telephone unit can make contact with a person having a conventional telephone line, and vice versa, even though the cellular telephone unit is not connected directly (with an installed telephone line) to the regular telephone network.
Cellular telephone units are highly portable, and are most frequently used within automobiles. Cellular units may be used anywhere within the RF "range" of the cellular network, whether used from a stationary or mobile location. Further, cellular units may be used without knowing precisely where they are located. All that is required for a cellular unit to be used is that it be able to receive and send signals from and to an established cellular telephone network.
Because a cellular telephone unit is highly portable, and may be readily moved from one location to another without affecting its operation, the use of a conventional cellular telephone unit in an EHAM system, e.g., to couple the FMD to the host computer via the established cellular telephone network, would create a serious problem. That is, if the person being monitored is supposed to remain within a prescribed distance of the FMD, e.g., 150 feet, a portable phone link, such as would be provided by a cellular unit, would allow the monitored individual to go anywhere within the cellular network range simply by picking up and carrying the FMD and cellular unit with him. Thus, what is needed is a cellular unit that can be coupled to an FMD, thereby allowing the EHAM function to be carried out without an installed (hard-wired) telephone line, but that can also detect and report any attempts to move the cellular unit.
Further, because a conventional cellular unit allows its user to freely access any desired telephone number by simply dialing the desired number, and because an effective EHAM system requires full-time accessibility to the host computer, there is a need for restricting a cellular unit used with an EHAM system to access only one telephone number--that telephone number coupled to the host computer.
Thus, it is evident that before a cellular unit could effectively be used as an interface between an FMD, or equivalent, and a host computer coupled to a conventional telephone line of an EHAM system, thereby allowing the EHAM function to be carried out at a house arrest location that does not have a hard-wired telephone line, there is a need to prevent, or at least detect and report, any movement of such cellular interface unit. Further, there is a need to restrict the telephone numbers that could be called by such cellular interface unit. Moreover, it would be desirable to detect and immediately report any unauthorized opening, or other tampering, of the cellular interface unit. The present invention advantageously addresses these and other needs.